Mechanical properties in the initial stage of sintering

Silicon nitride-based ceramics with different compositions were sintered in the 60%–90% range of theoretical density. Linear correlations between the apparent density and the modulus of elasticity, the three- and four-point bend strengths or the Vickers hardness, were observed. The slopes of the straight lines were nearly the same for all compositions. Furthermore, the modulus of elasticity, hardness, fracture toughness and strength were calculated as functions of density by modelling the structure as a random arrangement of spheres as suggested by Fischmeister and Arzt. The relationships obtained have been compared with the measured ones.Nomenclature a average contact area - a _c increase of the area of a crack - A area of the reference plane - b size of the critical defect - c constant in Equation 4 - D density - D ₀ density before shrinkage - D _T theoretical density - e direction of macroscopic strain - E modulus of elasticity - E ₀ modulus of elasticity of the dense material - f force loading a contact - f() projection of force f to e - F force loading the reference plane - g geometry parameter in the Griffiths relationship - H hardness - K _IC fracture toughness - N number of particles in unit volume - N() the fraction of N in a given spherical angle - n() number of particles in the volume around the reference plane - P porosity - R initial particle radius - R particle radius after fictitious growth - R particle radius after redistribution of material - R _SQ shared correlation coefficient - S surface energy of the defect - vector connecting the centres of neighbouring particles - W work necessary for increase the area of a crack - Z average coordination number - Z ₀ initial coordination number - strain - _T strain at theoretical strength - strength - _T theoretical strength (limit of elasticity) - angle between v and e     

Effect of Boron and Heat Treatment on Mechanical Properties of White Cast Iron for Mining Application

 Heat treatment methods were applied to white cast iron for improving the impact and wear resistance. Additionally, chemical composition optimization was made. Furthermore, the effect of boron addition on such applications was investigated. Samples were investigated by using optical and electron microscope methods. Hardness, wear and impact tests were conducted. The results showed that the secondary carbides in the standard alloy were iron-enriched, needle-like carbides M3C when the boron-added alloy contained Fe23(C,B)6 type, globular secondary carbides. It was concluded that heat treatment B provided higher wear and hardness properties, compared to the standard heat treatment. Optimum mechanical properties were obtained by lower destabilisation temperatures and increasing temperature reduced the wear resistance and hardness.     

Synthesis and photopolymerization of novel,highly reactive phosphonated-urea-methacrylates for dental materials

An urea methacrylate (1) and two phosphonated methacrylates (2–3) were synthesized from 2-isocyanatoethyl methacrylate (IEM) and benzyl amine (1), diethyl aminomethylphosphonate (2) and diethyl amino(phenyl)methylphosphonate (3). Their photopolymerization rates are notably higher than commercial monomers, despite the presence of only one double bond. Their polymerization rates follow the order 1 ～ 2 > 3 ～ triethylene glycol dimethacrylate (TEGDMA) > 2-hydroxyethyl methacrylate (HEMA). A tendency toward high crosslinking density during thermal bulk polymerizations, low oxygen sensitivity and high conversions with benzophenone during photopolymerization indicated the importance of hydrogen abstraction/chain transfer reactions. It was found that the addition of the monomers to HEMA significantly increased its polymerization rate, proving their utility as replacements for TEGDMA as reactive diluents for 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propyloxy) phenyl] propane (Bis-GMA). Copolymer systems containing 2 and 3 showed improved T_g values compared to Bis-GMA/TEGDMA systems.     

Acceleration of direct volume rendering with programmable graphics hardware

We propose a method to accelerate direct volume rendering using programmable graphics hardware (GPU). In the method, texture slices are grouped together to form a texture slab. Rendering non-empty slabs from front to back viewing order generates the resultant image. Considering each pixel of the image as a ray, slab silhouette maps (SSMs) are used to skip empty spaces along the ray direction per pixel basis. Additionally, SSMs contain terminated ray information. The method relies on hardware z-occlusion culling and hardware occlusion queries to accelerate ray traversals. The advantage of this method is that SSMs are created on the fly by the GPU without any pre-processing. The cost of generating the acceleration structure is very small with respect to the total rendering time.     

Ground-State Properties and Collective Excitations in a 2D Bose-Einstein Condensate with Gravity-Like Interatomic Attraction

We study the ground-state properties of a Bose-Einstein condensate (BEC) with the short-range repulsion and gravitylike 1/r interatomic attraction in two-dimensions (2D). Using the variational approach, we obtain the ground-state energy and show that the condensate is stable for all interaction strenghts in 2D. We also determine the collective excitations at zero temperature using the time-dependent variational method. We analyze the properties of the Thomas-Fermi-gravity (TF-G) and gravity (G) regimes.